if you are adding memory with the exsiting memory, the speed is 2133MHZ

[Trebuin]

Not sure about crucial, I used a lot crucial SSD disks before, the ssd disks did have more fault rate than other brands.

I'm actually looking at getting lower CL ram for the iMac, but we need to remember that you cannot mix different CL memory or the computer will have to adjust. That's possibly what you're seeing there. you can check the actual detail status by running bootcamp & CPU-X I think it is. I bought OWC CL11 ram only to find out they actually sent me CL17 ram...they were selling it as CL11 until just after the iMac release. There is a test of the HyperX memory correctly configured & it gives a boost for rare configurations.

 

[SaSaSushi]

I'm actually looking at getting lower CL ram for the iMac, but we need to remember that you cannot mix different CL memory or the computer will have to adjust.

Yes, as I already explained, it will adjust by running at the CAS latency of the slowest installed module.

Similarly, since the Kingston HyperX is actually overclocked 2133MHz RAM, when installed along with the non-overclocked 2400MHz RAM shipped with the system, it clocks back all system RAM to 2133MHz.

Again, there is probably a very good reason Apple clearly states the required RAM frequency and not the CAS latency for upgrade memory.

Also, CL11 as opposed to CL17 is not going to make any detectable difference in performance outside of bench tests.

 

[Trebuin]

Yes, as I already explained, it will adjust by running at the CAS latency of the slowest installed module.

Similarly, since the Kingston HyperX is actually overclocked 2133MHz RAM, when installed along with the non-overclocked 2400MHz RAM shipped with the system, it clocks back all system RAM to 2133MHz.

Again, there is probably a very good reason Apple clearly states the required RAM frequency and not the CAS latency for upgrade memory.

Also, CL11 as opposed to CL17 is not going to make any detectable difference in performance outside of bench tests.

Luckily, my encoding work has always benefited from lower CL, though we're talking a small 5-10%. Most applications don't.

 

[Blazer5913]

I just want to thank the original poster as well as @SaSaSushi for their input on this problem. I previously spent nearly an entire morning reading through the HUGE thread on "What memory to get for my new iMac" only to come out of that in a haze and have ZERO clue what to buy. But thanks to the original poster for asking the question, and all the responders, for bringing this issue up and clearing things up for me. It all makes sense now about the CL differences, the HyperX overclocked speeds, and the most important matter in this being the frequency of the RAM - aka just stick to DDR4 2400 and you will be fine. Appreciate it. Now just eventually have to click the "purchase" button one of these times I BTO a new iMac. Currently typing this on an older 2011 27" iMac i5 with non-retina, non-flash/fusion HDD and 8gb of RAM. I can't wait

 

[mathemabeat]

Yeah, can't go wrong with Crucial ram. I just installed some in my new 27 inch iMac and works perfectly at 2400Mhz along with the apple ram.

I would def. avoid any of the flasher "gamer" ram because overclocked ram is usually what you find.

 

[Blazer5913]

Yeah, can't go wrong with Crucial ram. I just installed some in my new 27 inch iMac and works perfectly at 2400Mhz along with the apple ram.

I would def. avoid any of the flasher "gamer" ram because overclocked ram is usually what you find.

Do you mind sharing a link for the kind you bought? I tried Amazon crucial 2400 ddr4 but many of the comments/questions said it did not work on the new iMacs. My sense is that you have to buy specific type from crucial website itself? At least for now?

 

[mathemabeat]

Do you mind sharing a link for the kind you bought? I tried Amazon crucial 2400 ddr4 but many of the comments/questions said it did not work on the new iMacs. My sense is that you have to buy specific type from crucial website itself? At least for now?

I bought two of these:
http://www.microcenter.com/product/463500/4GB_DDR4-2400_(PC4-19200)_SO-DIMM_Memory_Module

I'm sure you can get them on Amazon and elsewhere too.

I opted to add just an extra 8gigs because I want to max the machine out to 64 gigs but not till ddr4 prices drop back down.

 

[macintoshmac]

No, I am sure I bought correct RAM from amazon, https://www.amazon.ca/gp/product/B01BNJL8I4/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

Just insert the new RAMs, 2400MHZ; 32G
Just have the original RAMs, 2400MHZ; 16G

merge them together, 2133 MHZ, 48G

Now, I just stay with 32G the new RAMs

It might just be a latency issue causing the Mac to register the other sticks as lower speed when mated to the original sticks. Match the specs properly and it should work.